My iMac (intel) stopped responding to keyboard and mouse, now have only silver screen. Help!

I have been googling and trying anything that I thought would not hurt my computer. I tried resetting PRAM four times, and then finally found this blog here on apple discussions:

https://discussions.apple.com/thread/5495027?answerId=23609027022#23609027022

I reset the SMC per that discussion, and TaDa!!! Everything worked worked. Also my screen is much brighter. Thank you Fearull. I don't know which or all of the fixes worked, but I thank everyone who contributed the " Reset PRAM" instructions because I didn't know about any of it and would have never gotten my computer back on my own. I love the Apple Discusion people.

SCSilverfox

I must report that my problem ended only for a few days. The freezing of the computer with nonresponsiveness to the mouse and keyboard and followed by the silver screen recurred----several times. Everything changed with my fourth or fifth reset of the PRAM.

I was resetting the PRAM and was waiting for the second sound of the computer (while still holding all four keys, the Command + Option + P + R. I heard only one sound and the screen became a gray linen look with a popup square asking for the language desired and a warning that I must agree to the terms of the software license.

There were diffenent languages floating across the screen - one of them said "Welcome".

The mouse did resond to the scroll bar within the popup square and "English" was highlighted. There was an arrow which I clicked. MacOS Utilities popped up and gave me the following choices:

Restore from Time Machine Backup

Reinstall MacOSX (new copy of Lion needed)

Get Help Online (Browse Apple Support to find help)

Disk Utility (Repair of erase a disk using Disk Utility)

My only viable obtion was to Restore from Time Machine Backup. This took more than 1 1/2 hours and I was able only to back-up to December 2, 2013 and it was January 16, 2014. Once the backup was completed, the linen screen returned with Mac OSX Utilities box again plus a whirling color sheel and broken up puzzle pieces of different languaged. No resonse to the mouse or keyboard. I Powered off the computer holding the power button.

After about a half hour I turned the computer back on. It was now working except I had lost everything from Dec 2, 2013 to 1/16/14. Mail had to update, and I lost my Photoshop license. I used the computer for a while, but but within a few hours the keyboard an mouse froze again. I tried one more force quit with the Power button and then Power On. The computer worked for a few hours but froze again and silver screen.

I gave up and will take my computer to be repaired by Apple.

I want to report back on this issue, especially since no one else seems to have had this problem; even the technician at the Apple Store did not know what the problem was.

It took 10 days to discover the problem but they finally decided it was the video card and my computer was fixed. One thing that I did not describe is that the silver screen had miniscule colored dots - blue, green, red - all over. It did not strike me as being important, but apparantly it was.